Hydraulic control system for 4-speed automatic transmission

ABSTRACT

A hydraulic control system for 4-speed automatic transmission which is controlled by torque control hydraulic pressure in regular succession and can provide a skip shift comprises a fluid pump (32), a pressure regulator valve (34) for regulating the line pressure generated at the fluid pump (32), a plurality of frictional elements (108, 62, 120, 84, 94, 100, 126) actuated by drive hydraulic pressure or reverse hydraulic pressure in accordance with the position of a valve spool of a manual valve (58), a first transmission control portion (D) having at least two valves (78, 86, 98) for supplying hydraulic pressure to at least one of the frictional elements, and a second transmission control portion (E) for selecting at least one of the frictional elements.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hydraulic control system for anautomatic transmission, particularly to a hydraulic control system for4-speed automatic transmission which can increase power train efficiencyby controlling line pressure and can improve the responsiveness ofshifting time during gear shifting.

2. Description of Prior Art

A conventional vehicle automatic transmission has a torque converter, amultiple stage transmission gear mechanism connected with the torqueconverter, and frictional elements actuated by hydraulic pressure forselecting one of the gear ratios of the transmission gear mechanism inaccordance with vehicle operating conditions.

The hydraulic control system provides actuating hydraulic pressurepressurized by a fluid pump and required to operate the frictionalelements and control valves.

A commonly used automatic transmission of a vehicle has a fluid torqueconverter which generally includes a pump impeller connected to anengine output shaft to be driven thereby, a turbine runner connected toan input shaft of the transmission, and a stator disposed between thepump impeller and the turbine runner, so that hydraulic fluid iscirculated by the engine driven pump impeller through the turbine runnerwith the aid of the stator which functions to deflect the hydraulicfluid from the turbine runner to a direction where the fluid flow doesnot disturb the rotation of the pump impeller when the fluid flows fromthe turbine runner into the pump impeller.

The automatic shift is achieved by the operation of frictional elementssuch as clutches or kick-down brakes at each gear ratios. Also, a manualvalve, the ports of which are converted by selecting a position of aselector lever, is designed to receive fluid from a fluid pump and tosupply the fluid to a shift control valve. In case of a 4-speedautomatic transmission, the shift control valve has a plurality of portscontrolled by an electronic control system.

One example of a hydraulic pressure control system of an automatictransmission for a vehicle is described in FIG. 10, which shows acircuit diagram of a conventional hydraulic control system comprising atorque converter 1 attached to an engine through the engine flexibleplate and rotating at engine speed for transmitting power of the engineto an input shaft of the transmission gear mechanism, a damper clutchcontrol valve 2 for controlling the application and release of a damperclutch to increase the power train efficiency inside the torqueconverter 1, a regulator valve 5 for regulating the output hydraulicpressure of the fluid pump 4 according to the automatic transmissionrequirements, and a reducing valve 6 for regulating the stable supply ofhydraulic pressure to a solenoid valve and the damper clutch controlvalve 2.

A manual valve 7, which is connected to an outlet of the fluid pump 4and is provided with the hydraulic pressure, is designed to deliver linepressure to the regulator valve 5 and a shift control valve. The manualvalve 7 is changed in position (P,R,N,D,2,L) by a shift lever as shownin FIG. 10.

A shift control valve 8, which is operated in response to two shiftcontrol solenoid valves A and B controlled by a transmission controlunit (not shown) is designed to transmit the hydraulic pressureselectively through a first-second speed shift valve 9, an end clutchvalve 10, a second-third and third-fourth speed shift valve 11, and arear clutch exhaust valve 12 to a front clutch 13, a rear clutch 14, alow-reverse brake 15, a kickdown servo brake 16, an end clutch 17, andthe like. An N-D control valve 18 to reduce the impact caused byshifting the selector lever from N range to D range is connected to therear clutch 14. An N-R control valve 19 to reduce the impact caused byshifting the selector lever from N range to R range is connected to thelow-reverse brake 15 via the first-second speed shift valve.

Also, a pressure control solenoid valve 20 is connected to a pressurecontrol valve 21 to reduce the shock produced by the control at the timeof shifting.

In such a conventional hydraulic circuit, two shift control solenoidvalves A and B to control the positions of the valve spool in the shiftcontrol valve 8 send the hydraulic pressure produced by the fluid pump 4to a first line D1, a second line D2, a third line D3, and a fourth lineD4. When manual valve 7 is shifted to the R range, the hydraulicpressure is supplied through a reverse line R1. Following is the briefdescription of shifting operation in the system.

When D range is selected by a shift lever, hydraulic pressure generatedby the fluid pump 4 is supplied to the manual valve 7 via a line L1, andsupplied to the shift control valve 8 and the first line D1 via a lineL2.

At a first speed of "D" range, both of the shift control solenoid valvesA and B are controlled to be "ON" by the transmission control unit(`TCU`), and therefore the hydraulic pressure passing through the shiftcontrol valve 8 is exhausted to effect no change on the position of thevalve spool. At the same time, the TCU makes the pressure controlsolenoid valve 20 switch "ON", and some of the hydraulic pressurereturning via the reducing valve 6 is exhausted.

Since the hydraulic pressure in the first line D1 is not supplied to thefirst-second speed shift valve 9, the hydraulic pressure is supplied tothe rear clutch 14 via the rear clutch exhaust valve 12 to actuate thesame.

At a second speed of "D" range, the TCU makes the shift control solenoidvalves A switch "OFF", and the hydraulic pressure is exhausted towardthe shift control solenoid valve B to move the valve spool and a plug ofthe shift control valve 8 rightward so that the hydraulic pressure fromthe manual valve 7 is supplied to the line D2.

Accordingly, the hydraulic pressure in the line D2 is supplied to theleft side of the first-second speed shift valve 9 to push the valvespool rightward in order to provide for a third speed. At this moment,the pressure control solenoid valve 20 is "OFF" state to keep thehydraulic pressure from being exhausted, and thus the hydraulic pressurefrom the fluid pump 4 is supplied to the left side of the pressurecontrol valve 21 via the reducing valve 6 and a hydraulic line L3 topush the valve plug therein rightward. Accordingly, the hydraulicpressure passing through the first line D1 returns to the first-secondspeed shift valve 9 via the N-D control valve 18.

Because the valve spool of the first-second speed shift valve 9 ispushed rightward, the hydraulic pressure which has passed through theN-D control valve 18 is supplied to the kick-down servo brake 16 toactuate the same, and the second speed is accomplished thereby.

At a third speed of "D" range, because TCU makes both of the shiftcontrol solenoid valves A and B switch "OFF", the hydraulic pressure iskept from being exhausted. And the valve spool of the shift controlvalve 8 is moved rightward further, and the valve plug remains stopped.

At this state, because the second and third lines D2 and D3 are openedsimultaneously, the hydraulic pressure passing through the second lineD3 and being supplied to the right side of the end clutch valve 10pushes the valve plug leftward and gets into the end clutch 17 toactuate the same.

The hydraulic pressure passing through the first-second speed shiftvalve 9 via the pressure control valve 21 passes through thesecond-third and fourth-third speed shift valve 11. Then, a portion ofthe hydraulic pressure acts to release the kick-down servo brake 16 andanother portion of the hydraulic pressure acts to actuate the frontclutch 13.

At this moment, the servo brake 16 at the second speed state is releasedby means of the hydraulic pressure supplied to the line connected to thefront clutch 13.

At a fourth speed of "D" range, because TCU makes only the shift controlsolenoid valve B switch "OFF", the valve spool of the shift controlvalve 8 is moved to the right farther than it is at the third speed toopen the fourth line D4.

Then the hydraulic pressure supplied to the left side of the rear clutchexhaust valve 12 pushes the valve spool rightward to cut off supplyingthe hydraulic pressure for actuating the front clutch 13 and thehydraulic pressure for releasing the kick-down servo brake 16.Accordingly, the kickdown servo brake 16 is actuated againautomatically, the end clutch 17 at the third speed state is actuatedalso, and the fourth speed is accomplished thereby.

When the shift selector lever is at the R range, the hydraulic pressurefrom the manual valve 7 is supplied to the right side of thesecond-third and fourth-third speed shift valve 11 via the rear clutchexhaust valve 12 to push the valve spool leftward, and thus thehydraulic pressure from the manual valve 7 is supplied to the frontclutch 13 and the low-reverse brake 15 and acts to release the kick-downservo brake 16 to reverse the vehicle.

In the above-mentioned automatic transmission control system, becausethe speed is shifted successively from the first speed to the fourthspeed and the same hydraulic pressure from the fluid pump is supplied intwo modes, or "DRIVE" and "REVERSE" ranges, even in high speed, it isimpossible to be converted to lower hydraulic pressure, which leads towaste of power efficiency. In a conventional hydraulic pressure controlsystem for controlling the forward four speeds it has not been possibleto make a skip shifting, which results in a slow response of a gearshifting during high speed drive. Further, since control hydraulicpressure for controlling the pressure control valve is supplied laterthan actuating hydraulic pressure for frictional elements, which alsoresults in a slow response of gear shifting.

SUMMARY OF THE INVENTION

The present invention aims to provide an automatic transmission systemfor a vehicle which can improve responsiveness of a gear shifting bycontrolling clutches with torque control hydraulic pressure first inorder to engage corresponding frictional elements, and next with drivehydraulic pressure to accomplish the gear shifting.

Another object of the present invention is to provide an automatictransmission system for a vehicle which can variably control linepressure in order to enhance the power train efficiency during drivingand enhance shift feeling when a manual valve is shifted.

Still another object of the present invention is to provide an automatictransmission for a vehicle which can provide a skip shift when swiftgear shifting is needed during driving in order to enhanceresponsiveness thereof.

In order to achieve above objects, the present invention provides ahydraulic control system for 4-speed automatic transmission comprising:a fluid pump generating hydraulic pressure when the engine is driven; apressure regulator valve properly changing the hydraulic pressure fromthe fluid pump during forward driving or reverse driving; a torqueconverter transmitting a driving force of an engine to an input shaft; aconverter control regulator valve for selectively supplying damperclutch actuating hydraulic pressure in order to increase powertransmission efficiency of the torque converter; a solenoid supply valvefor receiving line pressure from the pressure control valve andsupplying reduced pressure to a plurality of solenoid valves; a firstfrictional element commonly acts at all gear ratios; second, third,fourth, fifth, sixth, and reverse frictional elements at least one ofwhich is actuated at each gear ratios; a control switch valve forselectively supplying torque control hydraulic pressure in order toactuate the frictional elements of each gear ratios; a torque controlregulator valve for changing hydraulic pressure into torque controlhydraulic pressure and supplying the torque control hydraulic pressureneeded for actuating the frictional elements of each gear ratios to saidcontrol switch valve; first-second, second-third and third-fourth speedshift valves for shifting speed in accordance with vehicle speed byselectively supplying the torque control hydraulic pressure from saidcontrol switch valve or drive hydraulic pressure from said pressurecontrol valve to at least one of the frictional elements in response to"ON"/"OFF" and duty ratio combination of said solenoid valves; a secondspeed valve, a third speed valve, and a fourth speed band valve each ofwhich supplies actuating hydraulic pressure to one of said frictionalelements and supplies a portion of the actuating hydraulic-pressure toone of said speed shift valves corresponding to next gear ratio bytorque control hydraulic pressure or drive hydraulic pressure appliedthereto; and a manual valve for supplying line pressure regulated bysaid pressure regulator valve in accordance with position of a shiftselector lever to said speed shift valves or to the reverse frictionalelement.

Actuating hydraulic pressure is directly applied from said manual valveto said reverse frictional element via a first passage. A reverse clutchinhibitor valve for preventing hydraulic pressure from being applied tosaid fifth frictional element when the shift selector lever is shiftedfrom "DR" range to "R" range is provided in the first passage in orderto prevent damage of a power train.

Said torque control regulator valve is connected to said control switchvalve through a second passage and said control switch valve isconnected to said first-second speed shift valve through first andsecond torque control hydraulic pressure passages, and torque controlhydraulic pressure is selectively supplied to said first-second speedshift valve in response to signal of one of the solenoid valves forcontrolling said control switch valve.

Said first-second speed shift valve includes first and second ports forreceiving torque control hydraulic pressure from said control switchvalve; third and fourth ports for supplying drive hydraulic pressure tosaid first valve; fifth and sixth ports for supplying the torque controlhydraulic pressure to 2nd-3rd speed shift valve; and a valve spool forselectively controlling said ports.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a schematic hydraulic circuit diagram of a hydraulic pressurecontrol system in neutral range according to the invention.

FIG. 2 is an enlarged circuit diagram of a damper clutch control portionaccording to the present invention.

FIG. 3 is a circuit diagram of a torque control hydraulic pressureregulating portion according to the present invention.

FIG. 4 is a circuit diagram of a first speed shift control portionaccording to the present invention.

FIG. 5 is a circuit diagram of a second speed shift control portionaccording to the present invention.

FIG. 6 is a detailed view of a pressure control valve according to thepresent invention.

FIG. 7 is a table showing combination of the solenoid valve operationaccording to the present invention.

FIG. 8 is a table showing combination of the frictional elements at eachgear ratios according to the present invention.

FIG. 9 a graph showing operation of a pressure control valve accordingto the present invention.

FIG. 10 is a schematic view of a hydraulic control system for anautomatic transmission of the prior art.

DETAILED DESCRIPTION OF THE INVENTION

Following is the detailed description of a preferred embodiment of thepresent invention with reference to the figures wherein same numberingsystems are used to represent the same component parts.

FIG. 1 is a schematic view of a hydraulic pressure control systemaccording to the present invention, when "N" range is selected by theshift selector lever. The hydraulic pressure control system includes atorque converter 30 disposed between a crank shaft of an engine (notshown) and a transmission; a fluid pump 32 having a drive gear (notshown) rotating with a pump drive hub (not shown) of the torqueconverter and a driven gear in mesh with the drive gear; a damper clutchregulating portion A for selectly engaging a damper clutch (not shown)of the torque converter 30 by changing the hydraulic pressure from theoil pump 32 a torque control hydraulic pressure regulating portion B forreducing the pressure supplied to first and second solenoid valves S1and S2 in order to convert the drive hydraulic pressure from the fluidpump 32 into pressure needed for actuating clutches; a frictionalelement portion C of gear ratios; and first and second control portionsD and E.

Outlet of take fluid pump 32 is connected to a pressure regulator valve34 for changing line pressure when drive "DR" or reverse "R" range isshifted from neutral "N" range via a passage 36. This pressure regulatorvalve 34 is connected to a converter clutch regulator valve 40 forsupplying hydraulic pressure to the torque converter 30 via a passage 38and via a passage 42, where a converter feed valve 44 for selectivelypreventing the flow of the hydraulic pressure is mounted.

The valve spool of the converter clutch regulator valve 40 has adifferent position in accordance with signals of a fourth solenoid valveS4 electrically controlled by transmission control unit (not shown).Thus one of the passages 38a and 38b communicates with the passage 42and the converter clutch regulator valve 40 can selectively engage thedamper clutch of the torque converter.

The passage 36 is extended to be connected to the solenoid supply valve46 of the torque control hydraulic pressure regulating portion B inorder to reduce line pressure. And the reduced hydraulic pressure can besupplied to a control switch valve 50 and a torque control regulatorvalve 52 via the passage 48. A passage 70 is branched off from thepassage 48 and is connected to the pressure control valve 34 the valvespool of which is controlled by the fourth and fifth solenoid valves S4and S5 and to the converter clutch regulator valve 40 to supplycontrolled pressure.

The valve spools of the control switch valve 50 and the torque controlregulator valve 52 have different positions in accordance with sixth andseventh solenoid valves S6 and S7 controlled by TCU, respectively. Sincethe sixth and seventh solenoid valves S6 and S7 exhaust or cut off theflow of the hydraulic pressure from the passage 48, they can generate orrelease the hydraulic pressure applied to the valve spools of thecontrol switch valve 50 and the torque control regulator valve 52,respectively.

The passage 48 is extended farther at the solenoid valve S7 andhydraulic pressure can be supplied to the valve spool of the reverseclutch inhibiter valve 54, which is a safety valve for preventingreverse driving of the vehicle. That is, when the "R" range is shiftedby mistake the seventh solenoid valve S7 can exhaust the hydraulicpressure in accordance with TCU.

The control switch valve 50 is connected to the torque control regulatorvalve 52 via a torque control hydraulic pressure passage 56, thehydraulic pressure passing through the passage 56 is supplied from adrive hydraulic pressure passage 60 connected to the manual valve 58cooperating with a shift lever (not shown).

The drive hydraulic pressure passage 60 is connected to the torquecontrol regulator valve 52, to the first frictional element 62 of thefrictional element portion C of gear ratios, and to the first-secondspeed shift valve 64. This first-second speed shift valve 64 isconnected to the control switch valve 50 via first and second torquecontrol hydraulic pressure passages 66 and 68. Hydraulic pressure issupplied via one of the passages 66 and 68 in accordance with operationof the control switch valve 50.

In order to control the pressure control valve 34 and the convert crutchregulator 40, a control passage 70 communicating with the passage 48 isconnected to the first-second speed shift valve 64 and the 2nd-3rd speedshift valve 72, which is connected to 3rd-4th speed shift valve 74. The1st-2nd speed shift valve 64 is connected to a second speed clutch valve78 via the passage 76. The second speed clutch valve 78 is connected to2nd-3rd speed shift valve 72 via a passage 80 and is connected to thesecond frictional element 84 via passage 82. Hydraulic pressure from the1st-2nd speed shift valve 64 or from the second speed clutch valve 78 issupplied to the 2nd-3rd speed shift valve 72 and to a third speed clutchvalve 86, which is connected to the 3rd-4th speed shift valve 74 via apassage 90, which communicating with a passage 92 to supply hydraulicpressure to the third frictional element 94.

The 3rd-4th speed shift valve is connected to a fourth band valve 98 viaa passage 96. This fourth band valve 98 is connected to a fourthfrictional element 100 actuated at fourth speed via a passage 102.

The reverse clutch inhibiter valve 54 is connected to a manual valve 58via a passage 104 and is connected to reverse frictional element 108 viaa passage 106. The manual valve 58 is connected to the third speedclutch valve 86 via a passage 110, which communicates with a passage 112to connect the third speed clutch valve 86 to the second speed clutchvalve 78.

The second speed clutch valve 78 for receiving hydraulic pressure viathe passage 112 is connected to the fourth frictional element 100 via apassage 114, which communicates with a passage 102 connected to thefourth speed band valve 98. At the connecting point of these passages102 and 104 a shuttle valve 116 is formed to block one of the passages102 and 104 when the other of the passages 104 and 102 receiveshydraulic pressure.

A reverse inhibiter valve 54 is connected to a fifth frictional elementvia a passage 118 and at the connecting point of the passages 118 and 82a shuttle valve 122 is formed to interrupt one passage 118 and 82 whenthe other passage 118 and 82 is subject to hydraulic pressure,respectively.

A hydraulic pressure control valve 124 to retard operation or to reduceactuating hydraulic pressure is mounted at a passage connecting thesecond speed clutch valve 78 and the fifth frictional element 120.

FIG. 2 is an enlarged view of the damper clutch control portion A, FIG.3 is an enlarged view of the first transmission control portion D, andFIG. 5 is an enlarged view of the second transmission control portion.Now, the components of the FIGS. 3, 4 and 5 will be described.

As shown in FIG. 2, a pressure regulator valve 34 of the damper clutchcontrol portion A has first and second ports 130 and 132 for receivingthe hydraulic pressure from the fluid pump 32, a third port 134 forreceiving lower pressure than that from the solenoid supply valve 46, afourth port 136 for receiving the drive hydraulic pressure from themanual valve 58, a fifth port 138 for exhausting the hydraulic pressureto the fluid pump, and a sixth port 140 for supplying hydraulic pressureto the converter feed valve 44.

Said pressure regulator valve 34 has a valve spool 142 for selectivelyclosing said ports 130, 132, 134, 136, 138, and 140. The valve spool 142includes a first land 144 for closing the sixth port 140, a second land146 for closing the fifth port 138, and a third land 148 for receivingthe hydraulic pressure from the fourth port 136. An elastic member 150supports the valve spool 142 and pushes it rightward. A first hydraulicpressure detecting chamber 152 for applying a variable force to thevalve spool 142 is formed where the elastic member 150 is located. Atthe opposite side of the elastic member 150 with respect to the valvespool 142, a second hydraulic pressure detecting chamber 154 for pushingthe valve spool 142 to the left is formed.

Said converter feed valve 44 includes a first port 156 connected to thesixth port 140 of the pressure regulator valve 34, a second portconnected to the converter clutch regulator valve 40, and a third port162 for bypassing hydraulic pressure to the hydraulic pressure detectingchamber 160. The valve spool 164 of this valve 44 has a first land 166for receiving the hydraulic pressure from the hydraulic pressuredetecting chamber 160 and a second land 170 for supporting an elasticmember 168 for resisting the hydraulic pressure. The first land 166selectively closes the first port 156.

As shown in FIG. 3, a solenoid supply valve 46 of the torque controlhydraulic pressure converter portion B includes a first port 172 forreceiving the line pressure from the passage 36, a second port 174 forreducing and exhausting the hydraulic pressure from the first port 172,and a third port 176 for receiving the reduced hydraulic pressure fromthe second port 174. A valve spool 180 has a first land 178 forreceiving the hydraulic pressure from the third port 176, second andthird lands 182 and 184 for receiving hydraulic pressure from the firstand second ports 172 and 174, respectively, and an elastic member 186for regulating the position of the valve spool 180 in accordance withthe hydraulic pressure from the third port 176.

A torque control regulator valve 52 for converting drive hydraulicpressure into torque control hydraulic pressure by meads of thehydraulic pressure from the second port 174 of the solenoid supply valve46 includes a first port 188 for receiving the hydraulic pressure fromthe solenoid supply valve 46, a second port 190 for receiving thehydraulic pressure from the drive hydraulic pressure passage 60, and athird port 192 for converting the drive hydraulic pressure into torquecontrol hydraulic pressure and supplying it to the control switch valve50.

The hydraulic pressure applied to the first port 188 is formed bythe"ON"/"OFF" operation of the seventh solenoid valve S7. A valve spoolmoved by this hydraulic pressure is divided into first and second valvespools 198 and 200 supported by first and second elastic members 194 and196, respectively.

Between the first and second valve spools 198 and 200 both the elasticmembers 194 and 196 are mounted. Elastic force of the first elasticmember 194 is bigger than that of the second elastic member 196. Whenthe first valve spool 198 is moved to the left, the second elasticmember 196 is compressed.

Said control switch valve 50 includes a first port 202 connected to apassage 48, a second port 204 connected to the third port 192 of thetorque control regulator valve 52, third and fourth ports 206 and 208connected to the passages 66 and 68, respectively, in order to supplythe torque control hydraulic pressure from the second port 204 to the1st-2nd speed shift valve 64.

The valve spool 210 of this valve 50 for receiving hydraulic pressure:in accordance with the sixth solenoid valve S6 includes a first land 212where the hydraulic pressure is applied to the both sides thereof, asecond land 214 where the hydraulic pressure is applied to the rightside thereof, and third and fourth lands 216 and 218 supplying thehydraulic pressure from the second port 204 to either the third or thefourth ports 206 and 208.

As shown in FIG. 4, a 1st-2nd speed shift valve 64 of the firsttransmission control portion D includes first and second ports 220 and222 connected to the first and second torque control hydraulic pressurepassages 66 and 68, respectively, a third port 224 connected to a drivehydraulic pressure passage 60, a fourth port 226 for supplying the drivehydraulic pressure from the third port 224 or the torque controlhydraulic pressure from the second port 68 to a passage 76, a fifth port228 for supplying the hydraulic pressure from the first port 220 to the2nd-3rd speed shift valve 72, a sixth port 230 for supplying thehydraulic pressure from the second port 222 to the 2nd-3rd speed shiftvalve 72, a seventh port 232 connected to a solenoid supply valve 46 viaa passage 70.

The valve spool 274 selectively closes said seven ports 220, 222, 224,226, 228, 230, and 232 includes a first land 278 for receiving thehydraulic pressure from a first hydraulic pressure acting chamber 276, asecond land 280 for selectively closing the exhaust port EX, a thirdland 282 for opening and closing the first port 220 and the fifth port228, a fourth land 284 for selectively closing the second port 222, thethird port 224, or fourth port 226, a fifth land 286 for closing thethird port 224, and a sixth land 288 for receiving the hydraulicpressure in accordance with "ON"/"OFF" operation of the second solenoidvalve S2.

The hydraulic pressure applied to the sixth land 188 is formed at asecond hydraulic pressure detecting chamber 190. Sectional area of thesixth land 188 is larger than that of the fifth land 186. Thus, thevalve spool 274 is moved leftward when the second solenoid valve S2 is"ON".

The 2nd-3rd speed shift valve 72 includes first and second ports 292 and294 connected to the fifth and sixth ports 228 and 230 of the 1st-2ndspeed shift valve 64, respectively, a third port 296 connected to theseventh port 232 of the 1st-2nd speed shift valve 64, a fourth port 298connected to the second speed clutch valve 78 via a passage 80, a fifthport 300 for supplying the hydraulic pressure of the first port 292 orthe fourth port 298 to the third speed clutch valve 86, and a sixth port302 for supplying hydraulic pressure from the second port 294 to the3rd-4th speed shift valve 74.

The valve spool 304 of this valve 72 for selectively closing the ports292, 294, 296, 298, 300, and 302 includes a first land for closing thefourth port 298, a second land 308 for interrupting the communication ofthe first port 292 and the fifth port 300, a third land 310 for closingthe second port 294, and a fourth land 314 for the movement of the valvespool 304. The hydraulic pressure from the hydraulic pressure detectingchamber 312 in accordance with "ON"/"OFF" operation of the firstsolenoid valve S1 is applied to the left side of the fourth land 314 andthe hydraulic pressure from the third port 296 is applied to the rightside of fourth land 314.

The 3rd-4th speed shift valve 74 includes a first port 316 connected tothe sixth port 302 of the 2nd-3rd speed shift valve 72, a second port318 connected to the third port 296 of the 2nd-3rd shift speed valve 72,a third port 320 connected to the third speed clutch valve 86 via apassage 90, and a fourth port 322 for supplying hydraulic pressure-tothe fourth speed band valve 98.

The valve spool 324 of this valve 74 for selectively closing the ports316, 318, 320, and 322 includes a first land 326 for opening and closingthe first port 316, a second land 328 for opening and closing the thirdport 320, and a third land 332 for moving the valve spool 324. Thehydraulic pressure from the hydraulic pressure detecting chamber 330 inaccordance with "ON"/"OFF" operation of the second solenoid valve S2 isapplied to the left side of the third land 314 and the hydraulicpressure from the solenoid supply valve 46 is applied to the right sideof third land 332.

As shown in FIG. 5, the second speed clutch valve 78 of the secondtransmission control portion E includes a first port 334 connected tothe fourth port 226 of the 1st-2nd speed shift valve 64, a second port336 for supplying the hydraulic pressure from the first port 334 to thesecond frictional element 84 through a passage 82, a third port 338 forreceiving hydraulic pressure from the third speed clutch valve 86 in the"2" range and "L" range, and fourth and fifth ports 340 and 342 forsupplying hydraulic fluid from the third port 388 to the fifth andfourth frictional elements 120 and 100, respectively.

The valve spool 344 of this valve 78 for selectively closing the ports334, 336, 338, 340, and 342 includes a first land 346 for receiving thehydraulic pressure from the first port 334, a second land 348 foropening and closing the fourth port 340, and a third land 350 foropening and closing the fifth port 342. An elastic member 352 forresisting against the hydraulic pressure of the first port 334 ismounted on the valve spool 344.

The third speed clutch valve 86 includes a first port 354 connected tothe 2nd-3rd speed shift valve 72 via a passage 88, a second port 356 forsupplying the hydraulic pressure from the first port 354 to the thirdfrictional element 94 and to the 3rd-4th speed shift valve 74, a thirdport 358 connected to the third port 338 of the second speed clutchvalve 78, and a fourth port 360 connected to the manual valve 58 via apassage 110.

The valve spool 362 for selectively opening and closing the ports of thethird speed clutch valve 86 includes a first land 366 for opening andclosing the first and second ports 354 and 356, a second land 368 foropening and closing the fourth port 360, and a third land 370 where anelastic member 364 is mounted.

The fourth speed band valve 98 for supplying hydraulic pressure to thefourth and sixth frictional elements 100 and 126 includes a first port372 connected to the 3rd-4th speed shift valve 74 via a passage 96, asecond port 374 supplying the hydraulic pressure from the first port 372to the fourth frictional element 100, a third port 376 connected to themanual valve 58 via a passage 110, and a fourth port 378 for supplyingthe hydraulic pressure from the third port 376 to the sixth frictionalelement 126.

The valve spool 380 for selectively opening and closing the ports of thefourth speed band valve 98 includes a first land for opening and closingthe first and second ports 372 and 374, a second land 386 for closingselectively the third port 376 or the fourth port 378, and a third landwhere the elastic member 382 is mounted.

The reverse clutch inhibiter valve 54 has a pressure detecting chamber390 where hydraulic pressure is generated in accordance with "ON"/"OFF"operation of the seventh solenoid valve S7. The vale 54 includes a firstport 392 connected to the manual valve 58 via a passage 104 and a secondport 394 selectively communicating with the first port 392 in accordancewith the hydraulic pressure of the hydraulic pressure detecting chamber350.

The valve spool 396 for opening and closing the ports 392 and 394includes a first land 398 where the hydraulic pressure from thehydraulic pressure detecting chamber 390 is applied, a second land 400which has a smaller sectional area than the first land 398, and a thirdland 402 for receiving the hydraulic pressure from the second port 394.The reverse clutch inhibiter valve 54 has a bypass passage 404 forapplying the hydraulic pressure from the second port 394 to the firstland 398.

FIG. 6 is a detailed view of an embodiment of the hydraulic controlvalve 124 according to the present invention. The valve 124, whichretards the operation of the fifth frictional element 120 or reduces theactuating hydraulic pressure, includes first and second passagesconnected to the fourth port of the second speed clutch valve 78. Thefirst passage 406 has a hydraulic pressure retarding means 410 whichpermits one-way flow and retards the supply of hydraulic pressure. Thehydraulic pressure retarding means 410 has a chamber 412, where anelastic member with a ball 414 is mounted, of a larger diameter than thepassage 406. The second passage 408 has a exhausting means 418 which hasa chamber 420, which has a ball member 422, of larger diameter than thepassage 408. Said chambers 412 and 420 have sloped surfaces 424 and 426facing opposite direction thereof, respectively.

The hydraulic control system having above construction accomplishestransmission from 1st speed to 4th speed, a skip shift from 1st speed to3rd speed, and a skip shift from 2nd speed to 4th speed in accordancewith the table shown in FIG. 7, which will be described hereinafter.

First speed of "DR" range

When the shift lever is shifted from neutral, "N" range to "DR" range,transmission control unit controls the first and second solenoid valvesS1 and S2 to "ON" state and controls the rest solenoid valves S2, S6,and S7 to "OFF" state.

By this combination of the solenoid valves hydraulic pressure from thefluid pump 32 is supplied to the first port 172 of the solenoid supplyvalve 46 via the passage 36 and exhausted through the second port 174.Then hydraulic pressure is applied to both sides of the second and thirdlands 182 and 184. The hydraulic pressure from the second port 174returns to the third port 176 and pushes the valve spool 180 leftward.

If the pushing force toward the first land 178 overcomes the elasticforce of the elastic member 186, the valve spool 180 moves leftward andopening area of the second port 174 becomes smaller thereby regulatingline pressure exhausted. When the valve spool 180 moves farther to theleft and the second land 182 lies between the first port 172 and thesecond port 174, the second port 174 communicates with the exhaust portEX and the line pressure in the passage 48 is reduced.

While this reducing operation progresses, the pushing force to the firstland 178 becomes smaller than the elastic force of the elastic member186. Then the spool valve 180 moves to the right and the first port 172communicates with the second port 174. Line pressure regulated by theforegoing operation is applied to the first hydraulic pressure detectingchamber 152 via the third port 134 of the hydraulic pressure regulatorvalve 34 and applied to the left end of the converter clutch regulatorvalve 40.

When the fifth solenoid valve S5 is controlled with a low duty ratio,the hydraulic pressure of the first hydraulic pressure detecting chamber152 increases and pushes the valve spool 142 to the right. When thevalve spool 142 starts to move to the right, the second land 146 startsto close the first port 130 and a fifth port 138 and the all thehydraulic pressure from the fluid pump is used for transmission.

On the other hand, when the fifth solenoid valve S5 is controlled with ahigh duty ratio, the hydraulic pressure applied to the second hydraulicpressure detecting chamber 154 from the manual valve 58 through thepassage 60 and through the fourth port 136 moves the valve spool 142 tothe left. Then the first port 130 communicates with the fifth port 138and the hydraulic pressure from the fluid pump 32 returns back to thefluid pump 32. At this time, the hydraulic pressure applied to theconverter feed valve 44 through the sixth port 140 of the pressureregulator valve 34 selectively permits the engagement of the damperclutch in the torque converter 30 in accordance with the position of thevalve spool of the converter clutch regulator valve 40. The position ofthe valve spool is varied in accordance with duty control of thesolenoid valve S4.

Some of hydraulic pressure from the solenoid supply valve 46 through thepassage 48 is applied to the first port 202 of the control switch valve50 and acts on the valve spool 210. The other hydraulic pressure throughthe passage 48 is applied to the first port 188 of the torque controlvalve 52. Since the solenoid valves S6, S7 are controlled to the "OFF"state, the valve spool 210 of the control switch valve 50 is movedleftward by the hydraulic pressure applied to the first land 212, thusthe second port 214 communicates with the third port 206. Then the valveplug 198 of the torque control regulator valve 52 is moved leftward bythe hydraulic pressure applied to the first port 188 and moves the valvespool 200 via the first elastic member 194.

As a result, since the second port 190 connected to the drive hydraulicpressure passage 60 communicates with the third port 192, the drivehydraulic pressure from the manual valve 58 is exhausted to the thirdport 206 of the control switch valve 50 through the passage 56. Some ofthe drive hydraulic pressure from the manual valve 58 is directlyapplied to the first frictional element 62 and the first speed isestablished.

At this time, the hydraulic pressure exhausted to the third port 306 ofthe control switch valve 50 is applied to the first port 220 of the1st-2nd speed shift valve 64. Since the solenoid valve S2 is controlledto "OFF" state, the hydraulic pressure in the second hydraulic pressuredetecting chamber 290 of the 1st-2nd speed shift valve 64 increases andmoves the valve spool 274 to the right. Then the first port 220 isclosed by the third land 282 and the hydraulic pressure through thefirst torque control hydraulic pressure passage 66 can not flow throughthe valve 64.

1st-2nd speed of the "DR" range

As vehicle speed increases at a first speed, TCU controls the solenoidvalve S6 from "OFF" state to "ON" state and controls the solenoid valveS7 under duty control. Then the hydraulic pressure into the passage 56increases from zero.

Since the hydraulic pressure applied to the right side of the first land212 of the control switch valve 50 is released by this operation, thevalve spool 210 is moved to the right by the pressure applied to theleft side of the first land 212, thus the second port 204 and the fourthport 208 communicates with each other.

Therefore, the hydraulic pressure from the third port 192 of the torquecontrol regulator valve 52 via the passage 56 is applied to the secondport of the 1st-2nd speed shift valve 64 through the second torquecontrol hydraulic pressure passage 68.

At this time, since the solenoid valve S2 is "OFF", the valve spool 274of the 1st-2nd speed shift valve 64 moves to the right and the secondport 222 communicates with the fourth port 226. Then the torque controlhydraulic pressure applied to the second port 222 is applied to thefirst port 334 of the second speed clutch valve 78 through the fourthport 226 and through the passage 76.

As a result, since the valve spool 344 of the second speed clutch valve78 is moved to the right by this flow and the first port 334communicates with the second port 336, the torque control hydraulicpressure supplied through the passage 76 is applied to the 2nd-3rd speedshift valve 72 via the passage 80. And some of the hydraulic pressure isapplied to the second frictional element 84 via the-passage 82. Then the2nd speed is established by the cooperation of the first and secondfrictional elements 62 and 84.

2nd speed of "DR" range

When torque control hydraulic pressure is applied to the secondfrictional element 84 at said 1st-2nd speed of "DR" range, TCU makessolenoid valve S3 switch "OFF" and makes the hydraulic pressure in thefirst hydraulic pressure chamber 276 of the 1st-2nd speed shift valve 64rise.

By this control the valve spool 274 of the 1st-2nd speed shift valve 64is moved from the right to the left and this movement of the valve spool274 makes the solenoid valve S2 switch "ON", thus the hydraulic pressurein the second hydraulic pressure detecting chamber 290 rises. However,since the hydraulic pressure supplied to the seventh port 232 is appliedto the right side of the sixth land 288, consequently, the rightwardforce with respect to the valve spool 274 is bigger than the leftwardforce with respect to the valve spool 274.

By this operation, since the second port 222 communicates with the sixthport 230, torque control hydraulic pressure is applied to the 2nd-3rdspeed shift valve 72. And since the third port 224 communicates with thefourth port 226, drive hydraulic pressure is applied to the second speedclutch valve 78 via the passage 76, and thus drive hydraulic pressure isapplied to the second frictional element 82 under torque controlhydraulic pressure. As a result, the second speed is established.

2nd-3rd speed of "DR" range

As vehicle speed increases at the second speed, TCU makes the solenoidvalve S6 switch "OFF", which moves the valve spool 210 leftward. By thisoperation, the hydraulic pressure supplied from the torque controlregulator valve 52 through the passage 56 is applied to the second port204 of the control switch valve 50 and exhausted through the third port206 of the valve 50.

At this time, the hydraulic pressure from the third port 206 is appliedto the first port 220 of the 1st-2nd speed shift valve 64 via the firsttorque control hydraulic pressure passage 66. Since the valve spool 274of the 1st-2nd speed shift valve 64 is moved leftward by the "ON" signalof the solenoid valves S2 and S3, the torque control hydraulic pressureapplied to the first port 220 is applied to the 2nd-3rd speed shiftvalve 72 via the fifth port 228.

Since the spool valve 304 is moved to the right by "ON" signal of thesolenoid valve S1, the hydraulic pressure from the 1st-2nd speed shiftvalve 64 is applied to the first port of the third speed clutch valve 86via the first port of the valve 64 and via the fifth port 300 of thevalve 64.

At this time, since the valve spool 362 of the third speed clutch valve86 is moved rightward by the hydraulic pressure applied to the firstport 354, the hydraulic pressure from the first port 354 is exhaustedthrough the second port 356. A portion of the hydraulic pressure isapplied to the third frictional element 94 and makes it actuated.Another portion-of the hydraulic pressure is applied to the third port320 of the 3rd-4th speed shift valve 74 via the passage 90. The otherportion of the hydraulic pressure is applied via the passage 91 branchedoff from the passage 90, via the third port 376 of the fourth speed bandvalve 98, and via the fourth port 378 to the sixth frictional element126.

By this operation, the first frictional element 62 actuated by thehydraulic pressure from the drive hydraulic pressure passage 60 and thesecond frictional element 84 actuated by the hydraulic pressure from thesecond port 336 of the second speed clutch valve 78 are actuated bydrive hydraulic pressure. The third frictional element 94 and the sixthfrictional element 126 are actuated by torque control hydraulic pressurein order to control the 3rd speed.

3rd speed of "DR" range

When the 2nd-3rd speed is accomplished, TCU makes the solenoid valve 57switch complete "OFF" under a duty ratio and makes the solenoid valve S1switch "OFF". Then the valve spool 304 of the 2nd-3rd speed shift valve72 which was moved leftward at the 2nd-3rd speed moves rightward, closesthe first port 292, opens the fourth port 298 connected to the secondport of the second speed clutch valve 78, and makes drive hydraulicpressure be applied to the fifth port 300. By this operation, the thirdfrictional element 94 is actuated by drive hydraulic pressure in orderto accomplish a substantial 3rd speed.

3rd-4th speed of "DR" range

As vehicle speed increases at the 3rd speed, TCU makes the solenoidvalve S6 switch "ON" and controls the solenoid valve S7 with a dutyratio. By this operation, the second port 204 of the control switchvalve 50 communicates with the fourth port 208, and thus the torquecontrol hydraulic pressure from the torque control regulator valve 52via the passage 56 is applied to the second port 222 of the 1st-2ndspeed shift valve 64 via the second torque control hydraulic pressurepassage 68.

At this time, since the solenoid valves controlled to be "OFF", thevalve spool 274 of the 1st-2nd speed shift valve moves leftward. Thenthe second port 222 communicates with the sixth port 230 and the thirdport 224 communicates with the fourth port 224.

Therefore, the torque control hydraulic pressure from the second port isapplied to the second port 294 of the 2nd-3rd speed shift valve 72 viasixth port 230. At this time, the valve spool 304 of the 2nd-3rd speedshift valve 72 is moved rightward by "OFF" signal of the solenoid valveS1 and the second port 294 communicates with the sixth port 302. Thetorque control hydraulic pressure supplied to the second port 294 isapplied to the first port 316 of the 3rd-4th speed shift valve.

Also, "OFF" signal of the solenoid valve S2 moves the valve spool 324 ofthe shift valve 74 to the right and the torque control hydraulicpressure supplied to the first port 16 is exhausted through the fourthport 322. The torque control hydraulic pressure exhausted through thefourth port 322 is applied to the first port 372 of the fourth speedband valve 98 via the passage 96 to move the valve spool 380 to theright, and applied to the fourth frictional element 100 via the secondport

The drive hydraulic pressure supplied to the third port 224 of the1st-2nd speed shift valve 64 is applied to the second speed clutch valve78 via the fourth port 226 and via the passage 76. Then the second port336 of the second speed clutch valve 78 is opened and a portion of thehydraulic pressure actuates the second frictional element 84. The otherportion of the hydraulic pressure is applied to the third speed clutchvalve 86 through the fourth and fifth ports 298 and 300 of the 2nd-3rdspeed shift valve 72 and through the passage 88.

The drive hydraulic pressure supplied to the third speed clutch valve 86pushes the valve spool 362 and a portion of the drive hydraulic pressureactuates the third frictional element 94.

As a result, the first, second, and third frictional elements 62, 84,and 94 are actuated by drive hydraulic pressure and the fourthfrictional element 100 is actuated by torque control hydraulic pressure.The sixth frictional element 126 is not actuated.

4th speed of "DR" range

When the 3rd-4th speed is accomplished, TCU makes the solenoid valve S2switch "ON". Then the valve spool 324 of the 3rd-4th speed shift valve74 moves leftward.

By this operation, the first port 316 for receiving the torque controlhydraulic pressure from the 2nd-3rd speed shift valve 72 is closed. Andthe third port 320 can communicate with the fourth port 322, whereby thedrive hydraulic pressure from the third speed clutch valve 86 is appliedto the third frictional element 94 and a portion of the hydraulicpressure is applied to the 3rd-4th speed shift valve 74 via the passage90.

Therefore, the fourth frictional element 100 which was actuated by thetorque control hydraulic pressure is actuated by drive hydraulicpressure and the 4th speed is established.

"R" range

In order to reverse the vehicle, the shift selector valve should beshifted to "R" range and the fifth frictional element 120 and thereverse frictional element 108 should be actuated.

When the shift selector valve is shifted to "R" range, a port forsupplying hydraulic pressure from the manual valve 58 to the drivehydraulic pressure passage 60 is closed and a port connected to thepassage 104 opens. The line pressure from the pressure regulator valve34 is directly applied to the reverse frictional element 108 and thereverse frictional element 108 is actuated.

At the same time, the reverse hydraulic pressure through the passage 104is applied to the first port 392 of the reverse clutch inhibiter valve54. Since the solenoid valve S7 is controlled with a low duty ratio, theposition of the valve spool 396 of this valve 54 is maintained at theleft side as viewed from the drawings.

Therefore, the reverse hydraulic pressure supplied to the first port 392of the reverse clutch inhibiter valve 54 is applied to the fifthfrictional element 120 which is a low reverse clutch, via the secondport 394 and via the passage 118 and actuates it.

At this time, TCU controls the solenoid valve S5 and increase linepressure needed for reverse driving.

1st-3rd skip shift of "DR" range

During driving at 2nd speed, when the throttle valve opens wider, TCUmakes the solenoid valve switch "OFF" and makes the solenoid valve S6switch "ON". Then the hydraulic pressure from the torque control valve52 via the passage 56 is exhausted via the second and fourth ports 204and 208 of the control switch valve 50.

And then the hydraulic pressure from the fourth port 208 of the controlswitch valve 50 is applied to the second port 222 of the 1st-2nd speedshift valve 64 via the second torque control hydraulic pressure passage68. At this time, since the solenoid valve S2 is "ON" and anothersolenoid valve S3 is "OFF", the valve spool 274 is moved to the rightand the second port 222 communicates with the fourth port 226.

Therefore, the torque control hydraulic pressure from the second port222 is exhausted via the fourth port 226 and applied to the first port334 of the second speed clutch valve 78 via the passage 76.

At this time, the hydraulic pressure applied to the first port 334 movesthe valve spool 344 to the right and is applied to the second frictionalelement 82 via the second port 336 and via the passage 82. A portion ofthe hydraulic pressure is supplied to the third frictional element 94through the fourth and fifth ports 298 and 300 of the 2nd-3rd speedshift valve 72, through the passage 80, thorough the first port 354 ofthe third speed clutch valve 86, through the second port 356 by movingthe valve spool 362 to the right, and through the passage 92. Andanother portion of the hydraulic pressure is applied to the sixthfrictional element 126 via the passage 90 and via the third and fourthports 376 and 378 of the fourth speed band valve 98.

By this operation, the hydraulic pressure is directly supplied to thefirst frictional element 62 from the drive hydraulic pressure passage60. Consequently, the transmission from the 1st speed where only onefrictional element is actuated to the 3rd speed where four frictionalelements are actuated is rapidly accomplished.

3rd-1st skip shift of "DR" range

While driving at 3rd speed, when a swift speed up is necessary, 3rd-1stskip shift is accomplished. At this time, the operation principle is thesame as the 1st-3rd skip shift, but it is done in reverse sequence. Theshock resulting from the down shift is reduced by a one-way clutch ofpower train.

2nd-4th skip shift of "DR" range

If the throttle valve opens rapidly at 2nd speed, TCU makes the solenoidvalve S1 switch "OFF", the solenoid valve S2 switch "ON", and thesolenoid valve S6 switch "OFF"

By this operation, the hydraulic pressure from the torque controlregulator valve 52 is supplied through the passage 56, through thesecond and third ports 204 and 206, and through the first torque controlhydraulic pressure passage 66 to the first port 220 of the 1st-2nd speedshift valve 64.

Since the solenoid valve S3 is "OFF", the valve spool 274 movesleftward. Then the first port 220 communicates with the fifth port 228and the hydraulic pressure from the first port 220 is applied to thefirst port 292 of the 2nd-3rd speed shift valve 72 through the fifthport 228 of the 1st-2nd speed shift valve 64.

At this time, since the solenoid valve S1 is "OFF", the valve spool 304of the 2nd-3rd speed shift valve 72 moves rightward and closes the firstport 292. Thus the torque control hydraulic pressure cannot pass thefirst port 292.

The drive hydraulic pressure from the drive hydraulic pressure passage60 is applied to the third port 224 of the 1st-2nd speed shift valve.Since the valve spool 274 is moved to the left by "OFF" signal of thesolenoid valve S3, the drive hydraulic pressure is exhausted through thesecond port 226 and is applied to the first port 334 of the second speedclutch valve 78 via the passage 76.

Since this pressure moves the valve spool 344 to the right and open thesecond port 336. The drive hydraulic pressure from the first port 334 issupplied through the second port 336 and through the passage 82 to thesecond frictional element 84. A portion of the hydraulic pressure issupplied through the passage 80, through the fourth and fifth port 298and 300, and through the passage 88 to the first port 354 of the thirdspeed clutch valve 86.

The hydraulic pressure applied to the first port 354 moves the valvespool 362 of the third speed clutch valve 86 to open the second port356. A portion of the hydraulic pressure applied to the third speedclutch valve 86 is applied to the third frictional element 94 via thepassage 88. Another portion of the hydraulic pressure is applied to thethird port 320 of the 3rd-4th speed shift valve 74 through the passage90.

Since the solenoid valve S2 is "ON", the valve spool 324 moves leftwardand the third port 320 communicates with the fourth port 322. Thus thehydraulic pressure from the passage 90 is applied to the first port 372of the fourth speed band valve 98 via the 3rd-4th shift speed valve 74and via the passage 96, thereby moving the valve spool 380 of the fourthspeed band valve 98 and opening the second port 374. That is, thehydraulic pressure from the passage 96 is applied to the fourthfrictional element 100 via the fourth speed band valve 98 and via thepassage 102.

At this time, the hydraulic pressure through the drive hydraulicpressure passage 60 is directly applied to the first frictional element62, and a skip shift from the 2nd speed when the two frictional elementsare actuated to the 4th speed when the four frictional elements areactuated is accomplished.

4th-2nd skip shift of "DR" range

While driving at 4th speed, when a swift speed up is necessary, 4th-2ndskip shift is accomplished. At this time, the operation principle is thesame as the 2nd-4th skip shift, but it is done in reverse sequence. Theshock resulting from the down shift is reduced by a one-way clutch ofthe power train.

FIG. 8 is a table showing combinations of the frictional elements; inorder to control the speed shifts in "DR" and "R" ranges. Since thespeed shifts in "2"and "L" ranges are achieved by the same combinationas shown in the table, the description of the speed shifts in thoseranges is omitted.

It can be understood that shifting from the 2nd, 3rd, and 4th speeds ofthe "DR" range to "L" range or shifting from the "2" range to "L" rangecause the fifth frictional element 120 and to be actuated. At this time,the control condition is that the hydraulic pressure applied to thefrictional elements which were actuated before shifting should beexhausted rapidly and time to supply initial actuating hydraulicpressure to the fifth frictional element 120 should be retarded.

In order to satisfy the above condition, the present invention providesthe hydraulic pressure regulator valve 124, the operation of which willbe described.

When the shift mode is changed from a certain mode to "L" range, thehydraulic pressure from the fourth port 340 of the second speed clutchvalve 78 is exhausted through the passages 406 and 408 and the hydraulicpressure from the fourth port 378 of the fourth speed band valve 98 isexhausted through the passages 406 and 408, as shown in FIG. 6.

At this time, the hydraulic pressure through the first passage 406 actson the ball member 414 and compresses the elastic member 410. Thus thehydraulic pressure is supplied into the chamber 412, simultaneously outto the opposite exit, and to the fifth frictional element 120. Hydraulicpressure into the second passage 408 can be supplied to the chamber 420,but is blocked by the ball member 422 there.

Since, at beginning of the inflow to the first passage 406, hydraulicpressure do not overcome elastic force of the elastic member 416,hydraulic pressure supply to the fifth frictional element 120 isretarded until the hydraulic pressure supplied to the first passage 406overcomes elastic force of the elastic member 416.

That is, after the actuating hydraulic pressure of the second frictionalelement 82 is exhausted, supply actuating hydraulic pressure to thefifth frictional element 120 is slowly achieved, as shown in FIG. 9.

Therefore, after the hydraulic pressure actuated at the previous stageis released, actuating hydraulic pressure for the new frictionalelements is supplied, which is good for preventing a tie-up phenomenonof the engine and reduce the shock caused by gear shifting by reducinginitial actuating hydraulic pressure.

FIG. 9 shows that actuating hydraulic pressure is supplied to the fifthfrictional element 120 after the second frictional element 84 isreleased. This is necessary to obtain an engine brake effect when manualshift from the 4th speed of "DR" range to 1st speed of "DR" range isaccomplished with "OFF" signal of the overdrive switch.

When shift selector lever is shifted from "DR" range to "R" range, thepower train is damaged by reverse driving force of the vehicle duringdriving. In this case, the solenoid valve S7 is controlled with a highduty ratio as an emergent means.

When the solenoid valve S7 is controlled with a high duty ratio, eventhough shift selector valve is shifted to "R" range, the valve spool 396of the reverse clutch inhibitor valve 54 moves rightward and closes thefirst and second ports 392 and 294. Thus, the hydraulic pressure fromthe manual valve 58 is supplied to the reverse frictional element 108via the passage 104. However, hydraulic pressure is not supplied to thepassage 118, and thus the fifth frictional element 120 is not actuatedand the reverse driving is not accomplished.

As described above, the hydraulic pressure control system for automatictransmission can minimize power loss of the fluid pump by controllingline pressure according to torque during gear shiftings, and thusenhance driving efficiency of the power train. Since speed shift beginswith torque control hydraulic pressure and ends with drive hydraulicpressure, the responsiveness of a gear shifting is enhanced. Further,since skip shift can be achieved, responsiveness of the automatictransmission when a swift speed up is necessary is also enhanced and theshock resulting from manual shift from 4th speed of "DR" range to "2"range or the manual shift from 3rd speed of "DR" range to "L" range canbe reduced. And since reverse driving is prevented during forwarddriving, it is safe. Still further, when shift selector lever is shiftedto "L" range or when an overdrive switch is "OFF" at 4th speed of "DR"range, engine brake effect can be achieved.

It will be evident to those skilled in the art that the invention is notlimited to the details of the foregoing illustrative embodiments andthat the present invention may be embodied in other specific formswithout departing from the spirit or essential attributes thereof. Thepresent embodiments are therefore to be considered as illustrative andnot restrictive.

What is claimed is:
 1. A hydraulic control system for 4-speed automatictransmission comprising:a fluid pump generating hydraulic pressure; apressure regulator valve properly changing the hydraulic pressure fromthe fluid pump during forward driving or a manual shifting; a torqueconverter transmitting a driving force of an engine to an input shaft; aconverter control regulator valve for selectively supplying damperclutch actuating hydraulic pressure in order to increase powertransmission efficiency of the torque converter; a solenoid supply valvefor receiving line pressure from the pressure regulator valve andsupplying reduced pressure to a plurality of solenoid valves; a firstfrictional element commonly acting at all forward gear ratios; second,third, fourth, fifth, sixth, and reverse frictional elements at leastone of which is actuated at each gear ratio; a control switch valve forselectively supplying torque control hydraulic pressure in order toactuate the frictional elements of each gear ratio; a torque controlregulator valve for changing hydraulic pressure into torque controlhydraulic pressure and supplying the torque control hydraulic pressureneeded for actuating the frictional elements of each gear ratio to saidcontrol switch valve; first-second, second-third and third-fourth speedshift valves for shifting speed in accordance with vehicle speed byselectively supplying the torque control hydraulic pressure from saidcontrol switch valve or drive hydraulic pressure from said pressureregulator valve to at least one of the frictional elements in responseto "ON"/"0FF" and duty ratio combination of said solenoid valves; asecond speed clutch valve, a third speed clutch valve and a fourth speedband valve for supplying actuating hydraulic pressure to one of saidfrictional elements and supplying a portion of the actuating hydraulicpressure to one of said shift valves for next gear ratio by torquecontrol hydraulic pressure or drive hydraulic pressure applied thereto;and a manually actuated valve for supplying line pressure, regulated bysaid pressure regulator valve, to said shift valves or to the reversefrictional element.
 2. A hydraulic control system for 4-speed automatictransmission according to the claim 1, wherein actuating hydraulicpressure is directly applied from said manual valve to said reversefrictional element via a first passage.
 3. A hydraulic control systemfor 4-speed automatic transmission according to the claim 1, wherein areverse clutch inhibitor valve for preventing hydraulic pressure frombeing applied to said fifth frictional element when the shift selectorlever is shifted from drive "DR" range to reverse "R" range is providedin a first passage in order to prevent damage of a power train.
 4. Ahydraulic control system for 4-speed automatic transmission according tothe claim 1, wherein said torque control regulator valve is connected tosaid control switch valve through a second passage and said controlswitch valve is connected to said first-second speed shift valve throughfirst and second torque control hydraulic pressure passages, and torquecontrol hydraulic pressure is selectively supplied to said first-secondspeed shift valve in response to signal of one of the solenoid valvesfor controlling said control switch valve.
 5. A hydraulic control systemfor 4-speed automatic transmission according to the claim 1, whereinsaid first-second speed shift valve includes first and second ports forreceiving torque control hydraulic pressure from said control switchvalve; third and fourth ports for supplying drive hydraulic pressure tosaid second speed clutch valve; fifth and sixth ports for supplying thetorque control hydraulic pressure to 2nd-3rd shift valve; and a valvespool for selectively controlling said ports.
 6. A hydraulic controlsystem for 4-speed automatic transmission according to the claim 1,wherein a pressure control valve including a first conduit for retardingsupply of hydraulic pressure and a second conduit for exhaustinghydraulic pressure is provided between said second speed clutch valveand said fifth frictional element.
 7. A hydraulic control system for4-speed automatic transmission according to the claim 6, wherein saidfirst conduit has a chamber where a ball member and an elastic membersupporting the ball member are provided.
 8. A hydraulic control systemfor 4-speed automatic transmission according to the claim 1, whereinsaid second speed clutch valve includes a first port for receivinghydraulic pressure from the first-second speed shift valve, a secondport for supplying the hydraulic pressure from the first port to saidsecond frictional element and said second-third speed shift valve, thirdand fourth ports for receiving hydraulic pressure from said manual valveand for supplying the hydraulic pressure to said fifth frictionalelement in reverse driving range, respectively, a fifth port forsupplying hydraulic pressure to said fourth frictional element in "2"range, and a valve spool having a plurality of lands for controllingopening all the ports of said second speed clutch valve.
 9. A hydrauliccontrol system for 4-speed automatic transmission according to the claim1, wherein said third speed clutch valve includes a first port forreceiving hydraulic pressure from said second-third speed shift valve, asecond port for supplying the hydraulic from the first port to saidthird-fourth speed shift valve, third and fourth ports for receivinghydraulic pressure from said manual valve and for supplying thehydraulic pressure to said second speed clutch valve, and a valve spoolhaving a plurality of lands for controlling opening all the ports of thesaid third speed clutch valve.
 10. A hydraulic control system for4-speed automatic transmission according to the claim 1, wherein saidfourth speed band valve includes a first port for receiving hydraulicpressure from said third-fourth speed shift valve, a second port forsupplying from the first port to said frictional element, and a valvespool having a plurality of lands for regulating all the ports of thesaid fourth speed band valve.